Java Multithreading, Concurrency, and Parallelism — Part 9

Synchronized on class objects and the scenarios of thread blockings

In Part-8 we have seen how the synchronized keyword works and its two bytecodes the monitorenter and monitorexit. But we have seen in the context of instance methods. Now we will see what happens with static methods.

NOTE: The words lock and monitor are used interchangeably here. Both are the same in our context.

With the static methods, the synchronization happens the same way except for the object on which the monitor is acquired. The lock/monitor is acquired on the class object.

When we use synchronized with the instance methods, the monitor is acquired on thethis object and when used with static methods the lock is acquired on the .class object.

Here is our Counter class with static synchronized methods.

And here is the bytecode snapshot of increment() method.